WAR, like any stat cannot be relied on as the be all end all. It's nice to use as a ballpark of comparing values of players, especially when there are multiple seasons of data to work with.
But at the same time, each of its components need to be looked at with a giant grain of salt. We often look at items like BAPIP, value with runners in scoring position, etc. to properly evaluate whether OPS or other stats of a player are a true reflection of that player's talent level. WAR doesn't do that for us. Defensively, you can look at players like Nyjer Morgan who happened to couple a great defensive WAR season with his best offensive season which saw him spike up the WAR leader charts. Was he really one of the best players in baseball during that season? Of course not.
WAR, like any stat, needs to be looked at with proper context. If a player really is elite defenisvely, looking at this year's defensive WAR as justification is not proper evidence. If a guy is truly elite defenisvely, it will show in numerous ways beyond WAR, and will do so for numerous seasons.
I prefer to use WAR when sample sizes have been properly set to remove the noise of year to year fluctuations, and when we are trying to compare players with different positions. I find it useful in trying to compare, say, who is a more valuable player, Buster Posey or Joey Votto? I like that WAR is able to compare positional value defensive value, offensive value, and baserunning all in one number. If used in proper context, it is a good way of measuring all of the components and assigning a number value to it. Otherwise, how else is it possible to assign a number value to a player's total production?
Like any stat, context is important. You can't determine the MVP of the season simply by looking at the WAR leaderboards at the end of the season because there are too many factors to consider. It's one piece of the puzzle, and if used correctly, I think it can be a very valuable piece of the puzzle. But I think at the same time it is not used in the proper way. Simply because Simmons and Gomez are at the of the list at the moment doesn't mean it is a useless stat. it just means that I think we need to apply some context to what it is telling us to be used appropriately.